The specification of U.S. Pat. No. 6,174,309 (Wrublewski) discloses an electrosurgical instrument in which tissue is sealed between the jaws of an end effector, before an electrosurgical signal is supplied to an electrosurgical cutting electrode in order to sever the tissue. In that instrument, the electrosurgical cutting electrode is movably biased against the tissue being severed. U.S. Pat. No. 7,033,356 relates to a more modern version of that instrument, in which tissue is tensioned across a jaw with a raised cross-section in order to assist in the severing of the tissue. The present invention provides an improvement to both of these earlier designs of instrument.